It has been shown that χ phage attacks almost all motile strains of Salmonella except the serotypes having H antigen
g…, l…, or
eh and certain strains having
1, 5 or
1, 2. So far, host range mutants of χ had been obtained against each of the resistant strains which have either H antigen
l…, eh, or
1, 2, but had not against those having
g antigen.
With serial mixed culture method, some new type phages which attack strains having
g antigen were isolated. The procedure was to cultivate χ phage together with a χ sensitive,
S. abortus-equi SL23, and one of the resistant strains. When the new type phage which can attack the resistant bacteria was not obtained from the mixed culture, the culture was centrifuged and an aliquot of the supernatant was used as the source of χ phage for the second mixed culture. This process was repeated until the new type phage was obtained up to the 10th subculture. Three new type phages were obtained from the serial mixed cultures in which each of NTCT8718, NTCT5723, and SJ26 was chosen as the resistant bacterial strain; they were designated M8, M12, and M26, respectively.
In one step growth of these phages in SL23, the latent period was about 60 minutes as that of the χ phage, and the average burst size was as follows: about 72 in M8, about 301 in M12, about 58 in M26, and about 110 in χ phage. From the K value test, it was showed that χ phage, M8, M12, and M26, were closely related in serological characters. When they were plated with SL23, the difference in plaque morphology could not be detected between χ phage and these new type phages. Similarity in the shape of these phage particles to χ phage was showed by electron microscopy. Host specificity to attack motile bacteria but not nonmotile bacteria was observed on these phages as well as on χ phage. These phages, however, differs from χ phage in their host range. They are able to attack a χ-resistant motile mutant strain, SJ100 derived from
S. typhimurium TM2, and several salmonella serotypes having H-antigen
g.
Host range mutants which attack SJ100 were isolated easily from χ phage. Among 106 such mutants (hT), two mutants (designated as hT94 and hT97) were able to attack
g-group Salmonella as the new type phages described above.
These results strongly suggest that these new type phages derived from χ phage passing through some spontaneous mutational steps; they may be multi-step host range mutants of χ phage. The Salmonella having H-antigen
g tested fall into three groups in regard to the responce to the host range mutants: (1) a type which allow the multiplication of phage, (2) a type which is lysed by infection but the lysis is not accompanied with the phage reproduction, and (3) a type which is not lysed. It is likely that the resistance of the Salmonella having H-antigen
g to χ phage consists of various numbers of complex factors including the antigenic type determinants.
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